Yes I keep meaning to try Clodhoppers suggestion - trouble is I only think of it when I'm preparing to re-light the fire in the evening when it's cold and dark so the ashes are just piling up by compost heap ATM.
Actually the shetland pony and even the sheep will eat rushes when they're hungry in the winter, but they don't do much in the summer when the rushes need cutting. And as for the brambles, if I flatten them (and chain harrow where possible) the sheep will strip them over the winter and are quite partial to the new leaves & shoots in the spring, so an annual flattening to keep them from growing into thickets seems to be working.
I am tackling the bracken/bramble with a mix of scything, rolling and harrowing, but due to the sheer size of the overgrown area that's only workable by hand (12 acres or so) I'm keen to try alternatives to mowing by hand or I'll still be working on it when I'm 100 yrs old.
The pigs enclosure does seem to be more open so they're having an effect. I considered reducing the available area as harmony suggested, but for now I'm going to wait and see what they do - It may take longer to clear but as long as it's getting clearer that's OK.